Scrap-melting,steelmaking vessel

ABSTRACT

The specification describes a method for producing steel utilizing scrap. A vessel suitable for use as a top-blown converter or an electric furnace is charged with scrap which is preheated in it and the vessel is then used for making steel. After this the vessel is again charged with scrap and the procedure is repeated.

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[54] SCRAP-MELTING, STEELMAKING VESSEL ABSTRACT: The specificationdescribes a method for producing steel utilizing scrap. A vesselsuitable for use as a top-blown converter or an electric furnace ischarged with scrap which is preheated in it and the vessel is then usedfor making steel. Afier this the vessel is again charged with scrap andthe procedure is repeated.

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SCRAP-MELTING, STEELMAKING VESSEL The invention relates to steelproduction and more particularly to electric furnace and top-blownconverter steelmaking processes utilizing scrap. Scrap has certaineconomic advantages over pig iron owing to its low price.

The amount of heat energy for producing liquid raw steel from steelscrap amounts to about 380 kcaL/kg. The overall energy requirement, thatis to say the requirement taking efficiency into account, for electricfurnaces is about 550 kwh./t. For the heating of steel scrap to aboutl,00O C. about half the amount of energy necessary for steel productionis required. The use of relatively expensive electric power isuneconomic in comparison with the costs to be expected if fuels such asoil or natural gas are used for heating up.

In order to reduce costs and increase output the use of cheap fuels forpreheating scrap has been repeatedly proposed for use in connection withvarious steelmaking methods. Thus, in Stahl und Eisen" 1967, pages 897to 903 the use of oil-ox ygen burners is described. This method was,however, not economically successful owing to the high cost ofcommercial quality oxygen. A further factor was that despite the use ofa high flame temperature the amount of the heat utilized was not morethan 50 percent owing to insufficient conduction into the mass of scrap.A better method is that described in the German specification 1,216,901in which the scrap is preheated from above in charging containers ofbasketlike construction, the products of combustion being drawn downthrough the scrap. After preheating the scrap was placed in an electricfurnace. However, with this method about one-third of the quantity ofheat is lost from the scrap.

In oxygen-blown converter processes the scrap makes up about 25 percentof the charge, the amount being limited by the amount of heat containedin the liquid iron and the amount of heat that can be released from itby chemical reaction. Any increase in the proportion of scrap, whichwould be economically advantageous, would require the supply ofadditional energy. Up till now it has been found that heating scrap aspart of a charge in a converter vessel using oxygen-fuel burners isexpensive as regards energy owing to the poor transfer of heat to thescrap.

The obvious idea of preheating the scrap before placing it in aconverter is found to be impracticable owing to the elaborate equipmentrequired and the amount of manipulation necessary to bring the hot scrapinto the converter.

One object of the present invention is to provide a method, which can beused both with electric furnaces and with converters or othersteelmaking apparatus employing a cruciblelike vessel, in which thescrap is heated to a high temperature, for example l,000 C., using cheapfuels and without the necessity of employing commercial quality oxygen.A further object of the invention is to provide such a process in whichheated scrap does not have to be transferred to another vessel.

The present invention consists in a method for producing steel in acruciblelike vessel comprising repeatedly carrying out the followingtwo-stage procedure:

1. preheating scrap in the vessel by means of a burner whose products ofcombustion are drawn through the scrap by suction, and

2. carrying out steelmaking in the vessel. In accordance with apreferred form of the invention two vessels are used together to carryout the stages of the method alternately so that parts of the equipmentnecessary such as electrodes (if the steel is to be made electrically),the pneumatic blowing arrangement (in the case of a convertersteelmaking process) and the preheating station can be used optimally.The vessel can be arranged to be moved from the preheating station tothe electrode or pneumatic refining station or in the case of astationary vessel the electrodes or pneumatic refining means and thepreheating means can be arranged to be moved.

Although, as inferred above, the important object of the invention is tomake the use of oxygen unnecessary, there may be circumstances, such aseconomic circumstances, which make it advantageous to use oxygen.

Cheap fluid fuels such as heating oil and natural gas are burned withcold or preheated air or oxygen-enriched air and the flames, or gases ofcombustion, are drawn down through the material to be melted. In thecase of cruciblelike vessel suitable drawoff openings can be provided.It is not possible to provide for sufficient drawoff through the bottomof such a vessel.

The invention is now described with reference to the accompanyingdrawings.

FIG. 1 is an axial section of a vessel with downwardly projectingburners and radially extending tubes near the bottom of the vessel fordrawing ofi products of combustion.

FIG. 2 is a further axial section of a vessel for carrying out theinvention in which exhaustion takes place through the lid of the vessel.7

FIG. 3 shows a still further vessel for carrying out the invention inwhich exhaustion takes place by means of a tube extending down from thetop of the vessel to a position near the bottom of the charge. 7

FIG. 4 shows a top-blown converter process making use of the method inaccordance with the invention.

FIG. 5 is a plan view of an electric steelmaking installation inaccordance with the invention.

FIG. 6 is a side view and section of the installation in accordance withFIG. 5. 7

As shown in FIG. 1 a crucible-shaped preheatingand steelmaking vessel 1in accordance with the invention is provided with a lid 2 used onlyduring scrap heating. Burners 3 project down through holes in the lid.In the sidewalls of the vessel there are suction openings 4 slightlyabove the level which will be assumed by the charge when it melts. Inorder to enhance the heating action of the products of combustion fromthe burners 3, tubes 5 extend radially inwards through the openings 4and slope downwards. The tubes 5 are provided with openings in theirwalls. The tubes 5 are connected witha suction means 6 which conveys theproducts of combustion to a chimney 7.

In the embodiment of the invention shown in FIG. 2 the products ofcombustion are drawn upwardly through the charge of the vessel 1 sincethe burners 3 are arranged to operate through openings at the bottoms ofthe sidewalls, while suction is applied through a duct to an opening 4in the center of the lid 2. Preferably the scrap charge is pressed inthe 'vessel so as to leave empty space 8 for the flames from theburners. The level which is assumed by the molten scrap in the vessel 1is denoted by a horizontal dot-dash line.

In converters for the pneumatic refining of the charge to produce steel,the burners and the suction tube are conveniently introduced from aboveinstead of through the sidewalls of the converter vessel. As shown inFIG. 3 the burners 3 are arranged in holes in the lid 2. A suction tube9 extends downwards and is connected by means of an elbow 10 to asuction means 6. The suction tube 9 is left in position after heatingthe scrap and is melted with it.

After heating of the scrap in the embodiment of the invention shown inFIGS. 1, 2 and 3, molten pig iron is brought into the vessel 1 andrefining is carried out electrically or by means of a hot blowing lance.

FIG. 4 shows the arrangement of a steelmaking vessel 1 on a bogie 11running on rails 12. The vessel 1 in the left-hand side of FIG. 4 hasthe removable lid 2 used for preheating placed on it. A burner 3projects its flame down into the vessel to preheat a charge of tons ofscrap in it. The volume occupied by the scrap is 80 cubic meters.Suction tubes for drawing the products of combustion down into the scrapare used but not shown in the drawing. Heating is carried out so as toreach a temperature of 900 C. After heating the converter vessel 1 andbogie 11 are moved into the position shown in the righthand side of FIG.4, this being the top-blowing station. Molten iron is placed in thevessel and top-blowing is carried out with a vertically movable tubularlance 13 using oxygen.

FIG. 5 is a plan view showing two steelmaking vessels In and lb.Reference numeral 114 denotes a column carrying an arm with burners 3for preheating scrap in the vessels. The burners can be swung fromvessel 1a to vessel lb. Reference numeral denotes electrodes forelectric steelmaking on an arm 16 which is pivoted on a column 17. Thevertical pivot axes of the electrodes 15 and the burners 3 are spacedfrom each other on a line 18 equidistant from the centers of the twosteelmaking vessels. Suction tubes in the converter are used but notshown.

FIG. 6 is a vertical section on the line VI-VI of FIG. 5, the means forpivotal mounting of the electrodes 15 and the burners 3 being omitted.

The invention is further illustrated by the following example.

EXAMPLE Use was made of two electric furnace vessels each having acapacity of 60 tons.

The time schedule of production in accordance with the example is asfollows:

Pro-heating in vessel in heating Vessel in electrode station for Theamount of scrap used is 66 tons. Fuel consumption for preheating thisamount of scrap to a mean temperature of 850 C. in 1 hour amounts to0.2Xl0 kcaL/t.

- For this procedure the economy in current is about 180 kwh./t. Thereis also a reduction in electrode consumption. This consumption is highin conventional electric furnace operation and amounts to about 2 kg./t.steel.

The time in which the transformer installation is actually in use isdoubled since operations which do not require the use of electrodes canbe largely carried out on the left-hand vessel.

Converters operated conventionally, that is without preheating, can use250 kg. of scrap per ton of steel produced. Preheating of the scrap to900 C. makes itpossible to increase the amount of scrap to 400 kg. perton. The fuel consumption for preheating is 0.25 10 kcal./t. scrap.Heating the scrap in vessels which are moved from one station to theother or are kept stationary and used with swinging heating and blowingmeans brings with it cost advantages over methods using less scrap andmore liquid iron, and the time required for scrap preheating does notreduce the output.

What I claim is:

1. In a steelmaking apparatus, in combination:

a. a crucible-shaped vessel having an open top and a bottom wallopposite said top;

b. a lid removably arranged on said vessel and covering said top, saidlid being formed with a burner opening;

c. a burner mounted at said opening, said burner being capable ofburning a fluid fuel and positioned for injecting the gases ofcombustion formed by said burning into said vessel; and

d. suction means for withdrawing said gases from said vessel, saidsuction means including a conduit extending inward of said vesselthrough an opening in the same remote from said top and having anorifice open to the interior of said vessel adjacent said bottom walland remote from said top.

2. In an apparatus as set forth in claim 1, said conduit slopingdownward from said opening toward said bottom wall and having an orificeremote from said opening.

1. In a steelmaking apparatus, in combination: a. a crucible-shapedvessel having an open top and a bottom wall opposite said top; b. a lidremovably arranged on said vessel and covering said top, said lid beingformed with a burner opening; c. a burner mounted at said opening, saidburner being capable of burning a fluid fuel and positioned forinjecting the gases of combustion formed by said burning into saidvessel; and d. suction means for withdrawing said gases from saidvessel, said suction means including a conduit extending inwArd of saidvessel through an opening in the same remote from said top and having anorifice open to the interior of said vessel adjacent said bottom walland remote from said top.
 2. In an apparatus as set forth in claim 1,said conduit sloping downward from said opening toward said bottom walland having an orifice remote from said opening.